Calutron ion source



Aug. 19, 1958 F. OPPENHEIMER 2,848,621

CALUTRON ION SOURCE 2 Sheets-Sheet 1 Filed Jan. 16, 1946 INVENTOR. Fran/ 0,0,08/7/76/7776f dim.

I f r 1 a 72' I 1 Patented Aug. 19, 1958 CALUTRON roN souncn Frank Oppenheimer, Berkeley, Calif., assignor to the United States of America as represented by the United This invention relates to means for ionizing material and is particularly concerned with means for ionizing material in an electric arc struck with the aid of a filament. Mechanisms of this general nature are exemplified in United States Patent No. 2,709,222 which issued to Ernest 0. Lawrence, May 24, 1955, for a mechanism referred to as a calutron. The particular portion of the showing in the mentioned Lawrence casewith which the present invention is principally concerned is especially disclosed in Figures 3 to of that patent.

The mentioned figures show an ion source block for containing material to be ionized. The material is heated, and as it emerges from the source block, or just prior to such emergence, is passed through an electric are that operates in the magnetic field of the calutron and extends between a filament serving as a cathode and the block or a plate serving as an anode.

Considerable difliculty has always been experienced in connection with the filamentary cathode. Various expedients have been tried from time to time in order to increase the life and durability of the filament. Some special difliculty arises due to the efiect of the magnetic field in imposing a force on the filament acting as an electric conductor. Other difficulties arise, apparently dueto the bombardment of the filament by returning positive particles from the are or adjacent the arc. In addition, it is, because of the relatively short life of a filament, desirable not only to lengthen the life as much as possible, but to facilitate the removal of spent or worn out or broken filaments, and to facilitate the introduction of replacement or new filaments.

In View of the foregoing circumstances, it is an object of the present invention to provide a filament having a mounting and configuration conducive to quick removal and change.

Another object of the invention is to alford a filament of a shape resistant to deflection by the magnetic field and having appropriate emitting characteristics.

An additional object of the invention is to provide means for protecting the filament from adverse bombardment.

An additional object of the invention is in general to provide a structure giving more satisfactory filament life.

An additional object of the invention is in general to improve the operattion of the ionizing arc in a calutron.

An additional object of the invention is in general to improve the operation of a calutron or comparable ionizing mechanism.

Other objects, together with the foregoing, will appear from the following description of the preferred embodiment of the invention that is illustrated in the accompanying drawings, in which:

Figure 1 is a side elevation of the source unit or ionizing mechanism of an exemplary form of calutron as shown in the identified figures of the Lawrence patent above referred to, certain portions of the structure being broken away and being shown in cross section to show the interior construction;

Fig. 2 is a plan of a part of the structure shown in Fig. 1, a portion of a cover plate being removed to disclose the interior arrangement; I

Fig. 3 is a cross section, the plane of which is indicated by the lines 33 of Fig. 2; and

Figs. 4, 5, and 6 show in plan block cover plates suitable for alternative incorporation with the structure of Figs. 1 to 3, inclusive.

In the preferred embodiment of the invention as shown in the accompanying drawings, a calutron is inclusive of an ion source unit, generally designated 6, disposed in the evacuated interior 7 of a tank defined by a side wall 8, a top wall 9, and a bottom wall 11. The tank is situated in a magnetic field established between an upper pole piece 12 and a lower pole piece 13 of an electromagnet.

The source block 6 is electrically insulated from the tank wall 8 and is supported at the end of a mounting stem 14, extending through an aperture 16 in the wall 8 of the tank and carried by a mounting and adjusting mechanism 17. This latter mechanism forms no part of the present invention, and is therefore not described herein in detail. The mechanism 17 is in turn supported on a framework 18 fastened to an electrical insulator 19, itself secured to the tank wall 8 by an appropriate fastening mechanism 21.

The inner end of the stem 14 is connected to the source block 6 by a thermal insulator 23, as the block 6 itself is preferably fabricated of athermally conducting material such as a metal, for example copper. Within the block 6 is disposed an electrical heating coil 24, supplied with energy by a lead 26 passing through the insulator 19 to an exterior source of energy. Adjacent the heater 24, in thermally conducting relationship therewith, is a gas distribution chamber 27, constituted by a cavity within the block 6 and having an outlet passage 28 to the interior of the tank 7.

Closing the upper end of the heater cavity 24 and the upper end of the gas distribution cavity 27 is a cover plate 29, secured by fastenings 31 and forming a support for a pair of filament leads 32 and 33 extending through the insulator 19 to a source of energy and terminating in grips 34 and 36 holding a filament 37 over an aperture 33 in the plate 29 and in registry with the passage 23. A securing block 40 holds the filament leads 32 and 33 in position, while the enclosure 41 of the filament is completed by a cap member 42, removably positioned by fasteners 43 operating through suitable apertures.

For supplying the gas distribution chamber 27 with a vapor or gas to be subsequently ionized, the block 6 is provided with a pair of cavities 46 and 47, each of cylindrical form and extending almost but not quite entirely through the metal of the block, so that heat from the source 24 is conducted to the walls of each of the cavities 46 and 47. The cavities communicate with the chamber 27 through outlet aperatures 48 and 49, respectively, so that gas flow from both chambers 46 and 47 to chamber 27 is readily effected. The two chambers 46 and 47 are simultaneously closed by a cover plate 51, preferably held removably in position on the block 6 by appropriate fastenings 52.

In especial accordance with the present invention, there is provided in addition to the cover plate over the block 6 an additional or supplementary restricting or collimating plate 61, extending for substantially the entire planar area of the lower portion of the housing 41 and having therein a perforation 62 or collimating aperature, disposed with the axis of the aperture substantially coincident or coaxial With the longitudinal axis of the ionizing or are passageway 28. The area or cross-sectional extent of the aperture 62 is substantially that desired for the ionizing arc, as it, in connection with the ambient magnetic field,

establishes a shape or contour and location for the arc. For that reason, it is referred to as a collimating plate.

Further in accordance with the present invention, the plate 61 can be replaced, if desired, by plates as shown in Figs. 5 and 6. In the case of the plate as shown in Fig. 5, there is afforded a collimating aperture 63, having not the customary circular configuration, but rather a rectangular configuration designed to produce an arc having a planar or flat face parallel to the exterior face of the source block 6. Alternatively, the plate shown in Fig. 6 may be utilized, as it is provided with an incomplete collimating aperture 64, this being constituted by a re-entrant notch formed in the material of the plate. This design is especially favorable when the plate material is difiicult to fabricate. For example, tungsten well serves as a collimating plate, but it is difi'icult to Work it except by some punching operations, and the design of the plate of Fig. 6 is especially applicable for use in such circumstances.

Also according to the present invention, the filament 37 is especially contoured, in that it has a pair of rectilinear end portions 66 and 67, each of which enters from the same respective side the associated one of certain grooves 68 and 69, formed in the grips 34 and 36, respectively, of the filament leads 32 and 33. Removable fastenings 71 and 72 clamp the filament ends in the grips 34- and 36. The intermediate or central portion of the filament 37 is convoluted into a helix or spiral 73 having a plurality of turns, so that the axis of the helix is substantially at right-angles or is perpendicular to the axis of the arc passage or chamber 28. Preferably, the helix 73 is so formed that one of the turns or convolutions is disposed directly over the subjacent collimating aperture 62.

When the cover member 42 is removed, the sides of the enclosed space 41 are exposed, as well as the fastenings 71 and'72, so that it is a simple matter to remove the filament and to replace it with another.

Pursuant to this invention, returning particles which might otherwise bombard the filament are substantially kept from the interior of the chamber enclosing the filament, stray vapor is substantially kept away from the filament, and the filament is protected generally from unwanted bombardment. The filament life is increased by the configuration and location of the filament, and the operation of the ionizing mechanism and calutron in general is greatly improved.

What is claimed is:

1. In a calutron having a strong magnetic field therethrough the combination comprising a source block having a gas ionization chamber therein, a pair of filament leads disposed adjacent to and overlying said block, filament gripping terminals on both of said leads, said terminals defining transverse grooves open at both ends, and a convoluted filament overlying said gas ionization chamber and having its opposite straight ends extending in the same direction parallel to the axis of the convoluted portion of the filament and entering both of said grooves from the same relative side thereof.

2. In a calutron the combination comprising means establishing a strong magnetic field, a source block having a gas ionization chamber therein and communicating with the exterior of said source block and disposed in said magnetic field, a filament enclosure mounted upon said source block and having an aperture therein communicating with said ionization chamber, filament leads extending into said enclosure, filament gripping terminals mounted upon said filament leads,.and a filament having a helical portion and straight end portions extending in the same direction, said filament being disposed with the helical portion in alignment with the aperture in said enclosure and secured in position by said filament gripping terminals engaging the straight end portions of said filament, and said enclosure having a removable wall whereby removal of said filament is facilitated.

Bleakney Nov. 12, l940 West Sept. 16, 1947 

